№3. Выполните действия: a)12$$\frac{7}{20}$$+7$$\frac{3}{20}$$-4; б)71$$\frac{8}{13}$$+8$$\frac{12}{13}$$+$$\frac{9}{13}$$; в)11$$\frac{21}{28}$$-9$$\frac{12}{28}$$+$$\frac{1}{28}$$;

Решение:

a) 12$$\frac{7}{20}$$+7$$\frac{3}{20}$$-4 = (12 + 7 - 4) + ($$\frac{7}{20}$$+$$\frac{3}{20}$$) = 15 +$$\frac{7 + 3}{20}$$ = 15 +$$\frac{10}{20}$$ = 15 +$$\frac{1}{2}$$ = 15$$\frac{1}{2}$$

б) 71$$\frac{8}{13}$$+8$$\frac{12}{13}$$+$$\frac{9}{13}$$ = (71 + 8) + ($$\frac{8}{13}$$+$$\frac{12}{13}$$+$$\frac{9}{13}$$) = 79 + $$\frac{8 + 12 + 9}{13}$$ = 79 + $$\frac{29}{13}$$ = 79 + 2$$\frac{3}{13}$$ = 81$$\frac{3}{13}$$

в) 11$$\frac{21}{28}$$-9$$\frac{12}{28}$$+$$\frac{1}{28}$$ = (11 - 9) + ($$\frac{21}{28}$$-$$\frac{12}{28}$$+$$\frac{1}{28}$$) = 2 + $$\frac{21 - 12 + 1}{28}$$ = 2 + $$\frac{10}{28}$$ = 2 + $$\frac{5}{14}$$ = 2$$\frac{5}{14}$$

Ответ: a) 15$$\frac{1}{2}$$; б) 81$$\frac{3}{13}$$; в) 2$$\frac{5}{14}$$